Digital video data is often processed and transferred in the form of bit streams. A bit stream is fine-grain scalable (“FGS”) if the bit stream can be decoded at any one of a finely spaced set of bitrates between pre-determined minimum and maximum rates. Unfortunately, this type of scalability typically results in a coding efficiency that is significantly less than that of a non-scalable video coder-decoder (“CODEC”).
The Moving Picture Experts Group (“MPEG”) has adopted standards for streaming video. The MPEG-4 standard includes a mode for FGS video. In MPEG-4 FGS video, the current frame is predicted using the minimum-bitrate reconstructed version of the previous frame. With MPEG-4, if a higher-bitrate version of the previous frame were used for prediction, this would lead to prediction drift any time the bit stream was decoded at a rate lower than the rate used for prediction in the encoder. The prediction drift is caused by the difference between the encoder's reference frame and the decoder's reference frame. Accordingly, it is desirable to improve the CODEC efficiency over that of typical FGS schemes such as, for example, the FGS video scheme adopted in the MPEG-4 standard.